6N01-7N01铝合金T型焊接接头的微观组织与性能的研究

The Heterogeneity in Microstructure and Property of the Welded Joints between 6N01 and 7N01 Aluminum Alloys

6N01和7N01铝合金是高铁列车车体上大量使用的2种重要的轻量化结构材料.本文利用EBSD、光学显微镜、维氏硬度测试和加速腐蚀实验研究了典型6N01-7N01铝合金T型焊接接头的微观组织、硬度分布和腐蚀特性.结果表明:焊缝、熔合区和热影响区的晶粒组织特征存在显著差异.焊缝组织为等轴晶,熔合区组织为等轴晶和柱状晶.靠近焊缝处的6N01合金存在部分晶粒异常长大现象,而7N01合金仅发生了回复和部分再结晶.6N01合金一侧的热影响区会出现硬度比焊缝更低的硬度谷,即软化区,这是由析出相受焊接热的影响发生明显的粗化导致的.经腐蚀实验后,焊缝的硬度显著降低,焊缝和热影响区为焊接接头腐蚀最严重的区域.

6N01 alloy and 7N01 alloy are two important lightweight structural materials for the applica- tion of high-speed railway body. The microstructure,hardness distribution and corrosion characteristics in a typical T-joint between TS-treated 6N01 alloy and TS-treated 7N01 alloy dissimilarly welded by metal-in- ert gas welding （MIG） was investigated by electron back-scattering diffraction （EBSD）, optical microscopy,Vickers hardness test and accelerated corrosion test. The results showed that there were sig- nificant differences in the grain structures between the weld seam, fusion zone and heat-affected zones. The weld seam had an equiaxed grain structure and the fusion zone consisted of equiaxed grains and columnar grains. In the region near the weld seam,abnormal grain growth was observed in the 6N01 part,while in the 7N01 part only recovery and partial recrystallization happened. In the heat-affected zones of the 6N01 part, there was a hardness groove, namely softening zone, the hardness of which was lower than that of the weld seam. The softening zone is attributed to obvious coarsening of precipitates affected by the heat input during welding. An obvious decrease in hardness occurred only in the weld seam after corrosion. In addi- tion, the corrosion attacks mainly happened in the weld seam and heat-affected zones.